North Wales police have said they have no idea why Perry Samuel took the lives of his children Caitlin and Aiden

Detective Superintendent John Chapman, who led the investigation into the murders, said: "We know that on that fateful day, the children’s mother had left the house in the morning to go to a concert in Manchester with some friends, and had planned for her to stay with them in a hotel.

"It was whilst back at the hotel following the concert she received a phone call from the police informing her of an incident at her home address.

"For three days following his arrest, Perry Samuel was interviewed regarding the events of that evening, and at no point did he acknowledge or give any account as to how the children met their deaths.

"He was able to provide detailed information with regards to their movements during the day, including going out for tea, but refused to provide the important details as to what happened and why.

"At no point did he ackowledge that he had killed the children and what triggered the incident.

"On the face of it, it had been a normal day, which on a Sunday usually led to the children having a bath before going to bed.

"Following his guilty plea, he clearly accepts he is responsible for the murders of his two children. Now he must do the right thing and tell Sarah exactly what happened and why - she needs to know, as do the children’s grandparents.

"Whilst they will have their own views on why this has happened, only Perry knows the truth.

"This will not change anything - however, it may help Sarah understand and know what the children went through and close a chapter in this nightmare that has been her life for the past four months.

"The ripples caused by the deaths of the children murdered by their father will be felt for years by Sarah, her family, their relatives and friends, and also by the community in Bodelwyddan.

"This has been a difficult case for me and the officers and police staff who have worked on the investigation.

"Yes, we have worked on far more complex cases where our joint investigation skills have been severely tested, but to work on a case involving such young innocent children provokes strong emotions in the hardest of individuals.

"Such cases are almost beyond comprehension and I know many people ask the question what could have been so awful in his life to make a father do this to his own children.

"There are many theories around regarding the phenomenon known as family annihilation, and one could put this case into the types of incidents which have been described as such.

"I would not want to make a judgement on whether this is one of those cases without first knowing what Perry Samuel’s account of this is.

"If and when he decides to do that, I will factually know what occurred that evening, but it will still be a comprehension why he did it."

DSI Chapman said Samuel himself had called the police, saying only: "There’s a problem with the children."

Samuel suggested at the time he had waited a number of hours after the children’s deaths before calling the police.

DSI Chapman said at no time during their questioning of Samuel did he show sadness or regret at his children’s deaths.

He said: "For somebody to show regret they have got to admit what they have done."